\input pstfig
\hskip 2cm
$
\setcoorunit{4}{1}
\psset{yunit=0.4\psxunit}
\psset{xunit=1.2\psxunit}
\drawaxes{-1.2}{3.2}{-5}{5.3}
\markxlabel{-0.5}{-\frac{\pi}{2}}{-1.5em}
\uput[-50](0,0){\scriptstyle O}
\markxlabel{0.5}{\frac{\pi}{2}}{1em}
\markxlabel{1.5}{\frac{3}{2}\pi}{1.5em}
\markxlabel{2.5}{\frac{5}{2}\pi}{1.5em}
\psplot{-0.42}{0.42}{1/cos(x*\pinum)}
\psplot{0.58}{1.42}{1/cos(x*\pinum)}
\psplot{1.58}{2.42}{1/cos(x*\pinum)}
\dashline\thinline
\psline(-0.5,4.4)(-0.5,-4.4)
\psline( 0.5,4.4)( 0.5,-4.4)
\psline( 1.5,4.4)( 1.5,-4.4)
\psline( 2.5,4.4)( 2.5,-4.4)
$
\bye
